Good summary Jorge. I think we will want to include any and all from anywhere. I had one other suggestion.

How about every person include two identical prints when the portfolio gets to them and then the next person in line keeps one of those prints and in turn includes two prints.

Example: I am the first person on the list. I mail the container to Brian with two of my prints. Brian keeps one and inludes two of his own. He mails to Jorge. Jorge keeps one of Brian's and includes two of his own. Next person keeps one of Jorge's prints and has the prints by Brian and me to view. He sends two prints to the next person who keeps one etc.
At the end of the cycle of 20 people, everyone has been able to view all the prints and have one to keep. The next time around you start with someone different so when the keeper comes around they will be from a different photographer.

This only means one extra print in the portfolio, but everyone exchanges a print with someone else, as well as viewing the work of those woh preceeded.

The only other question I think we need to finalize, is everyone going to send a print to one person first? This way everyone can see all the work at once and the first person would include two prints to get the exchange part rolling or,

Do we just begin with one person and build the portfolio overtime and after the first run through everyone will pull their "old" print and then include two new ones as it gets to them. This way the first person actually becomes the last because he is the final person to see the original portfolio before prints are switched out.

Sorry if this is somewhat rambling, I am short on time right now. Please add comments or critique of the above ideas.